Maya 3D - Mel Scripting.pdf - Autodesk Maya - Szycha20

MEL Scripting

Modeling Heads for Animation

A PPENDIX A

MEL Scripting

by Jesse Andrewartha and Matt Ontiveros

Introduction to MEL Scripting,” written by Jesse Andrewartha, is

a basic introduction to some MEL concepts. Jesse has added example

scripts for you to experiment with, along with explanations of tools

and descriptions of various MEL functions.This section of the appendix

gives you an idea of how Maya Embedded Language (MEL) is orga-

nized and provides insight into the proper syntax and operations of

MEL.

The second section, “Custom Window Control Setups,” is written by

Matt Ontiveros. It takes you to the next level of MEL, in that you can

put to use the introduction material of the first section to see how

MEL works for building a custom window and controls for a character.

The main thing to realize is that this chapter is an introduction to MEL

and is by no means the only approach to the tool.You should further

your study in this area of Maya by gathering as much information and

examples as possible in MEL and scripting.The more you use MEL, the

better you will understand its potential. Soon you will be able to write

your own scripts for your own projects that not only create solutions,

but ones that are truly unique.That is the goal of MEL.

T his appendix is divided into two parts.The first section, “An

maya 2 character animation

A.1 An Introduction to MEL Scripting

In a nutshell, MEL provides the foundation for Maya’s operation. It is

complementary to the base architecture of Maya. Although this might

seem a simple, singular concept, its implications are far reaching: MEL

allows unparalleled control over all aspects of the program. Incorporating

scripting into the animation workflow can greatly enhance productivity

as well as automate and create effects that are difficult and prohibitively

time consuming to complete with standard tools and workflows that are

common in Maya. From complex character animation and modeling

to special effects or rendering tools, MEL allows the user to increase

production speed and simultaneously create richer and more subtle

images and animation.With more than 600 commands and 75 functions,

MEL can be used to create custom effects, macros, custom GUIs, and

customization of Maya’s interface for particular scenes and requirements.

A.1.1 Writing MEL Scripts

There are three ways through which to write MEL scripts within the

Maya interface: the command line, the Script Editor, and the Expression

Editor.

A.1.1.1 The Command Line

The command line is visible in the UI immediately below the range

finder at the base of the screen.The command line, however, is limited to

displaying only one line of script at any given time and is therefore best

suited to single-line commands or procedures that reference larger

scripts.

appendix A: MEL scripting

Figure A.1

Located in the lower-left corner of the

Maya interface, the command line

allows simple execution of one-line

commands without having to open the

Script Editor window.

Command line

A typical example of a script used in the command line, to move a

primitive sphere, “Ball,” 90 degrees around the Z axis, would be written

in the command line as follows:

Rotate –r 0 0 90 Ball;

A.1.1.2 The Script Editor

In contrast, the Script Editor allows an almost limitless number of lines

and is most often preferred over the command line for writing out

complete scripts.

The Script Editor is specially designed to construct and execute MEL

scripts, and to record actions as they occur in the interface.To access

the Script Editor, select Window, General Editors, Script Editor.

maya 2 character animation

Figure A.2

Accessible either through the Windows

menu or by clicking the Script Editor

button, located in the lower-right side

of the Maya interface, the Script Editor

allows the execution of highly complex

scripts, and records all actions in MEL.

The Script Editor is also accessed from the UI, represented by a small

button immediately to the right of the playback controls at the base of

the screen.

The Script Editor is split into two parts.The bottom portion, or Input

Field, is used to enter MEL scripts, and the top portion, or History

Field, displays executed MEL scripts and the corresponding results or

errors.You can also use the Script Editor to save, import, and find script

files from your database.

When an action is executed using the Maya UI, the corresponding

MEL scripts used to carry out this same action are usually echoed in

the Script Editor’s History Field.To ensure that all MEL commands

are echoed to the Script Editor, click the option Echo All Commands,

which can be executed through Script Editor, Edit, Echo All

Commands.

This provides an excellent method to become familiar with MEL com-

mands; use the Maya UI to perform your work and observe the corre-

sponding MEL as it appears in the Script Editor.With the Echo All

Commands option on, the MEL commands for almost any action that

the user executes are displayed in the History Field. Note that there is

not always a one-to-one correspondence between what the user exe-

cutes and what is relayed to the Script Editor, regardless of whether the

Echo All Commands option is on or off. It is often useful to copy com-

mands out of the History Field and paste them in the Shelves or in the

Input Field (Shelves are discussed in more detail later in this chapter).

The copied script can be executed, or the information you need can be

pasted into other scripts to save time in typing.

A.1.2 The Expression Editor

You can also use the Expression Editor to execute MEL expressions.

Expressions are MEL scripts that use more than one command to create

an effect.The Expression Editor is specialized, however, and is usually

used only when applying commands to specific objects or their

attributes. It is also used to create Creation and Runtime expressions

when dealing with particles.

The Expression Editor is divided into two main sections.The upper

section is where you select the particular object and attribute to which

the expression will be applied. If you want to edit an expression, this

area can also list all the expressions active in the scene.The lower section

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